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The relationship between migration and natural
events is not straightforward and presents many complexities

Elevator pitch

The relationship between climatic shocks,
natural disasters, and migration has received increasing attention in recent
years and is quite controversial. One view suggests that climate change and
its associated natural disasters increase migration. An alternative view
suggests that climate change may only have marginal effects on migration.
Knowing whether climate change and natural disasters lead to more migration
is crucial to better understand the different channels of transmission
between climatic shocks and migration and to formulate evidence-based policy
recommendations for the efficient management of the consequences of
disasters.

Key findings

Pros

Migration can help people cope with the adverse effects of
climatic shocks by providing them with new opportunities and
resources.

Remittances from overseas migrants increase after disasters in
their home countries and play an important role in mitigating
the adverse effects of climatic shocks and natural
disasters.

Climatic factors, such as natural disasters or rainfall and
temperature variations, may increase international migration
through their effect on internal migration.

Agricultural productivity represents one of the pathways that
can explain the relationship between climatic shocks and
migration.

Public intervention both before and after disasters helps build
resilience and can explain why migration responses differ
according to different shocks.

Cons

The migration response to disasters depends on the nature of
the shock (slow vs rapid onset events), its severity, and the
vulnerability of the affected people.

Due to liquidity constraints, poor people might not be able to
migrate in the aftermath of climatic shocks.

In
developing countries, international migration due to disasters
may be driven by highly educated people, which may foster brain
drain in a vulnerable context.

Author's main message

Climate change and natural disasters cause
people to migrate if they do not have alternative mitigation strategies, are
forced to move because of the shock, and can afford migration costs.
Consequently, disaster management requires a holistic approach, where
migration and remittances, which are private mechanisms, should be
considered along with public intervention. In addition to helping households
build resilience by, for example, investing in infrastructure in vulnerable
areas, providing social protection, and allocating aid rapidly and
efficiently, better world governance is needed to reduce the human impact on
climate change.

Motivation

Climate change and
natural disasters are two of the biggest challenges for current
and future generations. Although the relationship between climatic factors
and migration has probably always existed, the mechanisms through which the
former impacts the latter are not yet fully understood. This is due to the
fact that their relationship is not straightforward and shows many
complexities. For policymakers, it is important to know what can motivate or
prevent people from migrating in the aftermath of a disaster. It is also
crucial to understand the role of the shock’s intensity as well as to
determine whether the relationship between climate change, natural
disasters, and migration is direct or affected by other factors. Moreover,
knowing if people engage in internal rather than international migration
would probably not have the same implications for the cost and affordability
of relocation, policy management of migrants, or the size of future
remittances. For all these reasons, empirical evidence is needed to inform
policymakers about the different migration responses to climate change and
natural disasters. This would help design better policies in terms of
protecting the most vulnerable populations from climatic shocks and their
consequences.

Discussion of pros and cons

Migration as a coping strategy for
climate change and natural disasters

The mitigating role of
migration

Population movement is a natural way to
deal with climatic shocks, particularly when livelihoods are
destroyed. Migration can be considered as an adaptation strategy
when disasters occur because it helps mitigate the adverse effects
of climatic shocks by providing new opportunities and resources to
affected people. It is also employed as a coping strategy when other
solutions have failed. For instance, in the case of drought,
potential solutions, which are also considered survival strategies,
can include changing consumption patterns by reducing the number of
daily meals, selling household assets, using food reserves, and
benefiting from solidarity through gifts, loans, and aid. Having
many possible coping strategies will reduce the likelihood of
migration due to shocks [2].

Between 2008 and 2014, developing
countries accounted for 95% of global displacement due to disasters.
Moreover, most of the displacements are from middle-income countries
(Figure 1). This is illustrative of the
fact that people at the extremities of the income distribution do
not necessarily migrate in the aftermath of disasters. Indeed, the
poorest cannot afford to migrate and the richest have other
mitigation strategies, such as the possibility to recover their lost
assets or better access to effective infrastructure and social
services, which allow them to cope with disasters without migrating.
Therefore, people at the middle of the income distribution are those
who do not have many alternatives at their disposal to deal with
adverse climatic shocks and, at the same time, can afford migration
costs.

However, it is important to point out
that the rather low rates of disaster-related migration from poor
and high-income countries does not necessarily mean that the poorest
and the richest people in a specific country do not migrate. There
is some heterogeneity within developing countries, which shows that
the level of vulnerability and the severity of the shock also matter
when it comes to the relationship between disasters and migration.
The level of vulnerability is correlated with factors such as the
risk of exposure to the shock, the level of poverty, the social
structure, the diversification of assets and income, and the
political situation. Indeed, people living in a politically unstable
environment have fewer survival strategies available to them than
those living in a peaceful one. The severity of the shock is
measured through the frequency, temporal spacing, and spatial
distribution of the event, and the way people affected perceive the
shock [2]. The frequency of shocks
represents the number of events in a given period. The temporal
spacing measures the elapsed time between two events. The spatial
distribution takes into account the extent of the shock in a given
region; for instance, an event that is isolated to a specific area
is easier to deal with than an event that affects an entire country.
Finally, the way people perceive the shocks is shaped by
expectations and experiences from previous events.

The role of vulnerability and severity
is highlighted in the case of Bangladesh over the period 1994–2010.
Moderate flooding, as compared to low levels of flooding, increased
an individual’s likelihood to move locally, but decreased his or her
likelihood to make a long-distance migration; this was especially
true for vulnerable groups such as the poor or women. Moreover,
households that were not directly affected by the flooding but lived
in areas with severe crop failure were more likely to move [3]. Figure 2 provides a good illustration of
how a disaster’s severity impacts population displacement. It shows
that displacements due to large-scale events represented 62% of
displacement in 2010. This is mainly due to the fact that
large-scale disasters occurred in 2010 with, for instance, the
earthquakes in Haiti and Chile and significant floods in China,
Columbia, Mexico, and Brazil. In 2014, just 32 large to very
large-scale events (accounting for less than 5% of all globally
recognized events) were the cause of 83% of total displacements.
Meanwhile, very small to medium-sized events represented 95.4% of
the total number of individual disasters but caused only 17% of the
total number of displaced people (Figure 3). This shows that very small
numbers of large-scale disasters can be responsible for a huge
portion of the displacement, while most disasters, which are
considered small- to medium-sized events, are responsible for far
fewer displacements.

The role of
remittances

Migration can also serve as a coping
mechanism through the remittances sent back by emigrants to
communities affected by climatic shocks and natural disasters.
Remittances help increase the resilience of households toward
natural disasters and reduce their vulnerability to the effects of
shocks. As migrants are, by definition, not present in their home
communities, their transfers provide insurance in case of shocks for
their left-behind relatives. Consequently, remittances help
households deal with income shocks caused by disasters.

An example from the Philippines shows
that transfers of money back home from international migrants
increase when natural disasters occur in their country of origin.
Filipino households with overseas migrants managed to completely
mitigate the income losses they suffered as a result of rainfall
shocks with the receipt of remittances; this was not the case for
households without overseas migrants [4]. In this context, it
would thus be important to find ways to reduce the cost of sending
remittances, which currently remain high, particularly in the case
of international migrants’ transfers.

Impact of climate change and natural
disasters on migration

Internal vs international
migration

Studies that look at the impact of
climatic factors on internal migration use the urbanization rate,
measured as a country’s share of urban to total population, as a
proxy for rural–urban migration due to the unavailability of
comparable internal migration data across countries and over time
[5], [6]. This is based on the
assumption that most internal population displacement is due to
rural-urban migration. However, evidence on the link between climate
change, natural disasters, and internal migration is rather mixed
and varies depending on the nature of the shock and across regions.
On the one hand, it has been found that natural disasters, defined
as short-term shocks, increase the urbanization rate in developing
countries [6]. On the other hand,
evidence shows that increasing temperatures, associated with
long-term events, positively affect internal migration in
middle-income countries but not in low-income countries, which is
related to liquidity constraints, as will be discussed later in the
article [5].

Evidence also shows that climatic shocks
and natural disasters could lead to international migration [1], [7], [8]. For instance, natural
disasters closely related to climate change such as storms, floods,
wet mass movements, drought, wildfire, and extreme high
temperatures, have been shown to boost migration from developing
countries to the six main OECD receiving countries: Australia,
Canada, France, Germany, the UK, and the US. Furthermore, this
effect is primarily driven by the migration of highly educated
people to these countries [1]. Education is correlated
with income, which may indicate that those highly educated people
can afford migration costs. This could also be interpreted to mean
that disasters related to climate change lead to brain drain from
developing countries, especially when the affected countries are in
a vulnerable situation due to the shock.

Another body of evidence finds that
climatic shocks such as weather anomalies affect international
migration through their effect on internal migration, which is
called an “economic geographic channel” [8]. For instance, in the
case of sub-Saharan Africa, weather anomalies are positively
associated with rural–urban migration because of their effects on
the agricultural sector. This internal migration, in turn, leads to
an increase in international migration because it raises the number
of workers in cities, translating into lower wages and increasing
people’s willingness to move internationally in search of higher
wages. Weather anomalies can also lead to high international
migration through a so-called “amenity channel” by increasing the
spread of disease and risk of death [8].

The positive relationship between
climatic shocks and migration, both internal and international, has
been challenged in the economics literature. There is some evidence
showing that climatic shocks do not necessarily lead to more
internal or international migration if the affected people are
burdened by liquidity constraints or if they have to deal with slow
onset events such as slowly changing temperatures [5]. Conversely, it might be
argued that when faced with rapid onset events such as cyclones,
storms, and floods, people could be forced to move because they lose
everything all at once, which is not necessarily the case with slow
onset events. Moreover, studies show that due to liquidity
constraints, victims of rapid onset events are more likely than
victims of slow onset events to make short-distance migrations [6] or short-term
relocations, rather than to embark on permanent or long-distance
migration [3]. For instance, a
large-scale analysis from Indonesia illustrates the impact of
long-term climatic shocks versus short-term disasters on different
types of migration. Considering internal migration (i.e.
province-to-province migration) of more than 7,000 households over
15 years, this study showed that natural disasters, which can also
be considered as rapid and sudden events, only have a marginal
effect on permanent outmigration to another province, while climatic
variations associated with slow onset events such as rainfall and
temperature variations increase permanent outmigration from a
certain threshold (25°C for temperature and 2.2m for rainfall), with
the effect of high temperatures being more important than that of
greater rainfall [9].

Indirect effects of natural disasters
on migration

Some studies have found that climatic
factors do not have any direct impact on migration, but an indirect one
[6]. One possible transmission
channel is agricultural productivity [5], [10]. This means that adverse
climatic shocks initially reduce agricultural productivity, which, in
turn, leads to increased migration.

Evidence from economic history provides a
good example of how negative climatic shocks affect population movement
through their effects in the agricultural sector. For instance, in the
agriculturally dependent plains counties of the US in the 1930s, large
dust storms due to prolonged severe drought conditions and intensive
land use caused permanent soil erosion. This phenomenon, known as the
American Dust Bowl, incurred substantial agricultural costs that were
mitigated, to a degree, by a relative population decline caused by
outmigration from high-erosion counties to low-erosion ones [11].

This example illustrates how disasters have
affected internal migration through their effect on the agricultural
sector. However, recent evidence shows that climatic shocks (i.e.
long-term events) can also affect international migration though
agricultural productivity. For instance, using bilateral annual
migration data from 163 origin countries and 42 destination countries,
which are mainly OECD countries, during the period 1980–2010, higher
temperatures have been found to increase international migration flows,
but only for countries that are highly dependent on agriculture [10].

The role of public intervention

Some disasters may increase migration flows,
while others do not have any impact on them; this might be explained by
the role of public intervention, both ex-ante and ex-post (meaning
before and after the event). Public intervention is crucial to reduce a
population’s vulnerability to climatic shocks and to improve their
resilience [12]. For instance, in the US in
the 1920s and 1930s, there were outflows of migrants from areas that
experienced a large number of tornadoes, while those affected by floods
had net inflows of migrants. The difference in migration responses in
the aftermath of tornadoes and floods can be explained primarily by the
early intervention actions of public authorities. Authorities invested
ex-ante in the infrastructure and protection of flood-prone areas, which
made them more resilient to shocks and improved their attractiveness as
living options. Such interventions did not happen in tornado-prone areas
[13].

More recently, in Bangladesh, over the
period 1994–2010, the occurrence of floods did not lead to high
migration from affected areas, while crop failure caused a dramatic
increase in migration. Again, the different migration reactions can be
attributed to authorities’ responses to the disasters; assistance was
provided in the aftermath of floods, while it was not the case for crop
losses [3]. Coping strategies for floods
have received more attention than for crop losses, both from researchers
and policymakers, at least in the case of Bangladesh. However, it
remains unclear why governments are generally more likely to invest in
flood-prone areas than those affected by other types of shocks. One
hypothesis is that floods are particularly destructive with respect to
housing and assets, whereas crop losses do not incur the same type of
losses. Given this tendency, it might be useful for governments to
expend more resources targeting populations affected by other types of
shocks such as crop failure.

Limitations and gaps

Although interest is increasing with respect to
the relationship between climate change, natural disasters, and migration,
both in the academic literature and among policymakers, it is still
difficult to achieve consensus on the exact nature of the relationship.
Consequently, there is, above all, a need for more evidence at the
microeconomic level. Long-duration panel data sets are needed to better
understand the long-term effects of disasters, though more efforts are
currently underway to address this issue. Having access to more information
on the socio-demographics of migrants in the aftermath of shocks as well as
knowing how people displaced due to climatic shocks and natural disasters
differ from conventional migrants such as labor migrants will help
researchers understand the consequences of disasters for both the origin and
destination areas. Additional information on the affected populations as
well as on those who relocate within their origin countries following a
post-disaster migration will also help shape specific policy intervention.
Finally, a crucial area for further research is to investigate the impact of
disaster-induced migration on the well-being of both migrants and those left
behind. This is particularly important because it could, for instance,
affect labor market outcomes in both origin and destination countries, as
well as inform on the integration of migrants in the receiving
countries.

Summary and policy advice

Natural disasters can occur anywhere; however,
developing countries are the most vulnerable to their effects. These
countries are unable to build up their resilience prior to the event or to
efficiently manage the post-disaster effects. Consequently, migration can
play an important mitigating role in the aftermath of natural disasters.
This role is reinforced by the impact of remittances, which help build
households’ resilience ex-ante and reduce the adverse effects of shocks on
their livelihoods ex-post. Disasters can lead to internal migration and,
depending on the circumstances, to international migration. People must be
able to afford to migrate; this makes liquidity constraints an important
element of the relationship between disasters and migration. Liquidity
constraints can also explain why people do not migrate in the case of slow
onset events. Moreover, even if people are forced to move, as is often the
case in rapid onset events, liquidity constraints may force them to relocate
only temporarily or embark on short-distance migrations. Disasters related
to climate can also impact migration through their effects on agricultural
productivity, typically by degrading crop yields. Finally, the evidence
shows that the type of policy interventions employed both before and after
disasters can explain why different disasters induce different migration
responses.

Migration and remittances, which are private
mechanisms for dealing with shocks, should be considered as complementary to
public intervention, and not as substitutes. If only migration and
remittances are available as mitigation strategies against disasters’
effects, this can lead to an increase in inequality between migrant
households and non-migrant households, as well as between remittance
receivers and non-receivers. Thus, disaster management requires a holistic
approach, which takes into account both private and public mechanisms for
protection and intervention. Governments should thus help channel migration
when necessary and alleviate the cost of sending remittances. Moreover,
ex-ante, public authorities can help households build disaster resilience
through, for instance, better social protections, effective insurance
mechanisms, and by diversifying the economy to reduce dependence on
agriculture. It is also important for governments to intervene rapidly and
to have strong institutions that can manage aid flows after disasters [12].

However, while it is largely accepted that
climate change and natural disasters are one of the main challenges of the
contemporary era, it is still difficult to achieve consensus on an
appropriate course of action, particularly between developed and developing
countries. Private solidarity mechanisms are at work—for example, in the
form of remittances—but there is a lack of solidarity between countries.
This raises equity issues because poor countries only play a small role in
driving the climate change process compared to developed ones, yet their
increased vulnerability exposes them more than richer nations to its adverse
effects. Thus, addressing the issue of climate change requires better
governance on a global scale, with more efficient aid allocated to
vulnerable countries as well as better migration policies toward migrants
from those countries. Migration in the aftermath of climatic shocks or
natural disasters should not be perceived as a threat for many reasons.
First, most migrants move internally or to neighboring countries. Second,
due to the prospect of remittances, migrants can help those left behind to
deal with shocks. Finally, migration remains a human right, above all in the
case of disasters related to the climate. Migrants should thus be received
and integrated into host societies, for the benefit of all.

Acknowledgments

The author thanks an anonymous referee and the
IZA World of Labor editors for many helpful suggestions on earlier drafts.
Previous work of the author contains a larger number of background
references for the material presented here and has been used intensively in
all major parts of this article [12]. Any opinions
expressed are those of the author and do not necessarily represent the views
of the African Development Bank Group or IZA.

Definition of climatic shocks and natural disasters

The term “climatic shocks” refers to variations
in rainfall and temperature over a long time period. While climatic shocks
suggest a long-term dimension of climate variability, “natural disasters”
are defined as short-term shocks, which happen suddenly and are mainly
unexpected. The main natural disasters considered are floods, earthquakes,
volcanic eruptions, landslides, droughts, tsunamis, storms or hurricanes,
extreme heat, water surges, water waves, and wildfires.Although climatic shocks and natural disasters
are the most frequently studied types of shocks when examining the effect of
environmental factors on migration, environmental deterioration has also
been considered, but only in a few studies. Environmental deterioration is
measured through deforestation, soil quality, sea level rise, air pollution,
soil erosion, overfishing, crop land, arable land, and crop failure.